Both twist-bits and drill-bits have the advantage over gimlet-bits in that they are less likely to split the wood.
Twist-bits and twist-drills are sharpened on a grindstone, care being taken to preserve the original angle of the cutting edge so that the edge will meet the wood and there will be clearance.
_German gimlet-bits_, Fig.

128, have the advantage of centering well.
The size is indicated on the tang in 32nds of an inch.

They are useful in boring holes for short blunt screws as well as deep holes.

They cannot be sharpened readily but are cheap and easily replaced.
_Bit-point drills_, Fig.

129, are useful for accurate work, but are expensive.
_Auger-bits_, Fig.